Center beam rail road cars, in cross-section, generally have a rack-like body, namely a center beam structure in the shape of an I in which the top flange is narrower than the bottom flange. The center beam structure is carried on a pair of rail car trucks. The rack, or center beam structure, has a pair of bulkheads at either longitudinal end that extend transversely to the rolling direction of the car. The lading supporting structure of the beam includes laterally extending decking mounted above, and spanning the space between, the trucks. A center beam web structure, typically in the nature of an open frame truss for carrying vertical shear loads, stands upright from the deck and runs along the longitudinal centerline of the car between the end bulkheads. This kind of webwork structure can be constructed from an array of parallel uprights and appropriate diagonal bracing. Most often, a top truss assembly is mounted on top of the vertical web and extends laterally to either side of the centerline of the car. The top truss is part of an upper beam assembly, (that is, the upper or top flange end of the center beam) and is usually manufactured as a wide flange, or wide flange-simulating truss, both to co-operate with the center sill to resist vertical bending, and also to resist bending due to horizontal loading of the car while travelling on a curve. Typically, a center sill extends the length of the car. The center beam thus formed is conceptually a deep girder beam whose bottom flange is the center sill, and whose top flange is the top truss (or analogous structure) of the car.
Center beam cars are commonly used to transport packaged bundles of lumber, although other loads such as pipe, steel, engineered wood products, or other goods can also be carried. The space above the decking and below the lateral wings of the top truss on each side of the vertical web of the center beam forms left and right bunks upon which bundles of wood can be loaded. The base of the bunk generally includes risers that are mounted to slant inward, and the vertical web of the center beam is generally tapered from bottom to top, such that when the bundles are stacked, the overall stack leans inward toward the longitudinal centerline of the car.
Lading is most typically secured in place using straps or cables. Generally, the straps extend from a winch device mounted at deck level, upward outside the bundles, to a top fitting. The top fitting can be located at one of several intermediate heights for partially loaded cars. Most typically, the cars are fully loaded and the strap terminates at a fitting mounted to the outboard wing of the upper beam assembly. Inasmuch as the upper beam assembly is narrower than the bundles, when the strap is drawn taut by tightening the winch, it binds on the upper outer corner of the topmost bundle and exerts a force inwardly and downwardly, tending thereby to hold the stack in place tight against the center beam web.
Each bundle typically contains a number of pieces of lumber, commonly the nominal 2″×4″, 2″×6″, 2″×8″ or other standard size. The lengths of the bundles vary, typically to ranging from 8′ to 24′, in 2′ increments. The most common bundle size is nominally 32 inches deep by 49 inches wide, although 24 inch deep bundles are also used, and 16 inch deep bundles can be used, although these latter are generally less common. A 32 inch nominal bundle may contain stacks of 21 boards, each 1-½ inch thick, making 31-½ inches, and may include a further 1-½ inches of dunnage for a total of 33 inches. The bundles are loaded such that the longitudinal axes of the boards are parallel to the longitudinal, or rolling, axis of the car generally. The bundles are often wrapped in a plastic sheeting to provide some protection from rain and snow, and also to discourage embedment of abrasive materials such as sand, in the boards. The bundles are stacked on the car bunks with the dunnage located between the bundles such that a fork-lift can be used for loading and unloading. For bundles of kiln dried softwood lumber the loading density is taken as 1600 to 2000 Lbs. per 1000 board-feet.
It has been observed that when the straps are tightened, the innermost, uppermost boards of the topmost bundle bear the greatest portion of the lateral reaction force against the center beam due to the tension in the straps or cables. It has also been observed that when these bundles bear against the vertical posts of the center beam, the force is borne over only a small area. As the car travels, it is subject to vibration and longitudinal inertia loads. Consequently the plastic sheeting may tend to be torn or damaged in the vicinity of the vertical posts, and the innermost, uppermost boards can be damaged. The physical damage to these boards may tend to make them less readily saleable. Further, whether or not the boards are damaged, if the plastic is ripped, moisture can collect inside the sheeting. This may lead to the growth of molds, and may cause discolouration of the boards. In some markets the aesthetic appearance of the wood is critical to its saleability, and it would be advantageous to avoid this discolouration.
In part, the difficulty arises because the bearing area may be too small. Further, the join between the upstanding web portion of the center beam and the upper beam assembly can coincide with the height of the topmost boards. This join is not always smooth. Further still, when the posts are fabricated the flanges may not stand perfectly perpendicular to the web, such that one edge of the flange may bear harder against the bundles than another.
It is also desirable that the bundles stack squarely one upon another. Although it is possible to use wooden battens at the top end of the center beam web, this will tend to cause the top bundle to sit outwardly of its neighbours. It has been observed that a thin wooden batten, of ¾″ thickness may tend to bow inwardly between adjacent posts, and may not spread the wear load as much as may be desired. A 1-½ inch thick wooden batten may have a greater ability to resist this bowing effect. However, the space available for employing a batten may tend to be limited by the design envelope of the car. Inasmuch as is advantageous to load the car as fully as possible, and given that the design of the car may usually reflect a desire to maximize loading within the permissible operational envelope according to the applicable AAR standard, the use of a relatively thick wooden batten may tend to push the outside edge of the top bundle outside the permissible operational envelope. Wooden battens may also be prone to rotting if subject to excessive exposure to moisture, or may be consumable wear items that may require relatively frequent periodic replacement.
It would be desirable to have an upper beam assembly that is integrated into the structure, that is formed to spread the bearing load across a larger area, that would tend to resist the bowing phenomenon, that would tend not to require frequent replacement, and that would tend not to be prone to rotting.
Existing center beam cars tend to have been made to fall within the car design envelope, or outline, of the American Association of Railroads standard AAR Plate C, and tend to have a flat main deck that runs at the level of the top of the main bolsters at either end of the car. In U.S. Pat. No. 4,951,575, of Dominguez et al., issued Aug. 28, 1990, a center beam car is shown that falls within the design envelope of plate C, and also has a depressed center deck between the car trucks. It would be advantageous to be able to operate center beam cars that exceed Plate C and fall within AAR Plate F, with a full load of lumber in bundles stacked 5 bundles high. A five bundle high load of 33 inch bundles requires a vertical clearance in the left and right hand bunks of at least 165 inches. This significantly exceeds the vertical loading envelope of a plate C car.
Increased vertical loading to exceed Plate C, as in a Plate F car, may tend also to increase the height of the center of gravity of a loaded car above the allowable vertical center of gravity height limit of 98 inches measured from top-of-rail (TOR). Consequently it may be desired to drop the center portion of the deck further to once again lower the center of gravity. However, as the deck is dropped further, the deck must also become narrower to remain within the AAR design envelope, whether of Plate C or Plate F. Further still, when the truck centers of the car exceed 46 ft. 3 in., the mid-span car width must be reduced due to swing out as the car travels through corners. That is, the car must lie within the design envelope of a 10′-8″ wide car with 46′-3″ truck centers, on a 13° curve (equivalent to a track center radius of 441.7 ft.). For a car having a nominal length of 73 ft, and a 56 ft well, will probably have a distance between truck centers of the order of 67 or 68 ft. The allowance for swing out, (that is, the reduction in width to match a car having 46′-3″ truck centers), for such a car is significant.
As the allowable car width becomes narrower, either due to increasing the truck centers beyond 46 ft. 3 in., or due to lowering the height of the decking, it is highly desirable to retain as much of the remaining lateral width as possible to support the bundles. Moreover, it has become desirable to provide a bunk width sufficient to carry 51 inch wide bundles, as well as 49 inch wide bundles. In the past, as shown in U.S. Pat. No. 4,951,575 winches have been installed outboard of the side sills at longitudinal stations corresponding to the longitudinal stations of the outboard ends of the cross bearers. These winches are used to cinch the strapping that is used to secure the load to the center beam top compression member wings, or, in the case of a partially loaded car, to the center beam main vertical web assembly. The winches tend to extend further laterally outboard, relative to the longitudinal centerline, than any other part of the car. Given the inwardly angled profile of the lower portions of the Plate C and Plate F envelopes, each incremental decrease in overall car width measured from the centerline to the outboard extremity of the winch permits an incremental lowering of the loaded center of gravity of the car. Consequently, it is advantageous to make the winch mounting as laterally compact as possible.
In known center beam cars, such as those shown in U.S. Pat. No. 4,951,575 and in U.S. Pat. No. 4,802,420 of Butcher et al., issued Feb. 7, 1989, the deck structure of the cars has included inwardly tapering risers mounted above the cross bearers, with longitudinally extending side sills running along the ends of the cross-bearers. The side sills have been angle or channel sections. In U.S. Pat. No. 4,951,575 the side sills are z-sections with the upper leg of the Z extending outward, the lower leg extending inward, and the web between the two legs running vertically. In U.S. Pat. No. 4,802,420 of Butcher et al., the side sill is a channel section, with the legs extending laterally outward and the web, being the back of the channel, extending vertically between the two legs. In both cases the winch is mounted outward of the vertical web.
In center beam cars it is desirable that the main center sill be aligned with the couplers to reduce or avoid eccentric draft or buff loads from being transmitted. In dealing with lateral loads, the side sills act as opposed flanges of a beam. The loads in the side sills, whether in tension, compression, vertical shear or lateral bending, tend to be transferred to the main sill through a main bolster assembly at each end of the car. In general the bolster is located at a level corresponding to the height of the main sill, and the shear plate, if one is used, is typically at a level corresponding to the level of the upper flange of the main sill.
It is desirable to have a well deck, also called a depressed center deck or dropped deck, between the trucks, to increase the load that can be carried, and so to increase the overall ratio of loaded weight to empty weight of the car, and also to reduce the height of the center of gravity of the car when loaded, as compared to a car having a flat, straight-through deck from end to end carrying the same load. In the case of a well deck, compression and tension loads in the side sills must be carried from the level of the side sills in the well, to the level of the side sills over the trucks, and then through the bolster structure and into the main sill. The transmission of forces through the vertical distance of the eccentricity of the rise in the side sills from the well to the bolster results in the generation of a moment. When the side sill has a knee at the transition from the well to the end structure of the car, the height of the knee defines the arm of the moment. It is advantageous not to create an unnecessarily large moment couple, and hence to keep the knee height small.
The coupler height of rail road cars is 34-½″ above top of rail (TOR). This is a standard height to permit interchangeable use of various types of rail cars. The main sill, or stub sill if used, tends to have a hollow box or channel section, the hollow acting as a socket into which the coupler is mounted. The minimum height of the main sill at the trucks (or stub sill, if one is used) and end structure bolsters tends to be determined by the coupler height, and the height required to clear the wheels. The height of the well deck is limited by the design envelope, be it Plate C, Plate F, or some other. In general, however, the height of the shear plate, or top flange of the bolster, to the well decking is less than the desired 33 inch bundle height. It is desirable for the top of the first layer of bundles stacked in the well to be at a height that permits the next layer of bundles to match the height of bundles stacked over the trucks. Consequently it would be advantageous to have a false deck, or staging, mounted above the shear plate, or if there is no end structure shear plate, then above the bolster, at a level to match the level of the top of the bundles carried in the well between the trucks.
One way to reduce the stress concentration at the knee is to make the side sill section of the end portion of the sill deeper. Another way to reduce the stress concentration at the knee is to make the knee member wider. On the longitudinally inwardly facing side of the knee (that is, the side oriented toward the lading in the well) the flange of the vertical leg of the knee may tend to extend perpendicularly. On the longitudinally outboard side, that is, the side facing the truck, the longitudinally outboard flange can be angled, or swept, resulting in a tapering leg, rather than one with parallel flanges. An increase in the section width, due to tapering the longitudinally outboard flange is desirable, as it permits a reduction in the stress concentration in the side sill assembly at the knee, and tends to provide greater truck clearance.
It may also be desirable or advantageous to be able to adjust the height of the structure over the bolster under circumstances where loads other than 33 inch bundles of lumber are carried, either by raising or lowering the staging to a different height, or lowering or removing it altogether such that the load is borne through the bolster and shear plate structure.